The family of ammonium transporters (AMT) in Sorghum bicolor: two AMT members are induced locally, but not systemically in roots colonized by arbuscular mycorrhizal fungi

Abstract

SummaryArbuscular mycorrhizal (AM) fungi contribute to plant nitrogen (N) acquisition. Recent studies demonstrated the transport of N in the form of ammonium during AM symbiosis. Here, we hypothesize that induction of specific ammonium transporter (AMT) genes in Sorghum bicolor during AM colonization might play a key role in the functionality of the symbiosis.For the first time, combining a split-root experiment and microdissection technology, we were able to assess the precise expression pattern of two AM-inducible AMTs, SbAMT3;1 and SbAMT4. Immunolocalization was used to localize the protein of SbAMT3;1.The expression of SbAMT3;1 and SbAMT4 was greatly induced locally in root cells containing arbuscules and in adjacent cells. However, a split-root experiment revealed that this induction was not systemic. By contrast, a strictly AM-induced phosphate transporter (SbPt11) was expressed systemically in the split-root experiment. However, a gradient of expression was apparent. Immunolocalization analyses demonstrated that SbAMT3;1 was present only in cells containing developing arbuscules.Our results show that the SbAMT3;1 and SbAMT4 genes are expressed in root cortical cells, which makes them ready to accommodate arbuscules, a process of considerable importance in view of the short life span of arbuscules. Additionally, SbAMT3;1 might play an important role in N transfer during AM symbiosis.

Phylogenetic, structural, and functional characterization of AMT3;1, an ammonium transporter induced by mycorrhization among model grasses

“…A mycorrhiza-inducible ortholog of AMT3;1 was also described for rice, another member of the Poaceae plant family (Perez-Tienda et al 2014). In cells containing developing arbuscules, a second AM-inducible AMT was described in sorghum, SbAMT4 (Koegel et al 2013a). But SbAMT4 was less induced compared to SbAMT3;1, suggesting a secondary role in the ammonium uptake through the periarbuscular membrane.…”

“…GinAMT3 is overexpressed in the intraradical mycelium under high-P conditions, indicating that more NH 4 + is transferred when the AM fungus has easy access to a P source. On the plant side, some AMTs have shown to be induced during mycorrhizal colonization as, for example, in Lotus japonicus (Guether et al 2009), Glycine max (Kobae et al 2010), Oryza sativa (Perez-Tienda et al 2014), Medicago truncatula (Breuillin-Sessoms et al 2015), or Sorghum bicolor (Koegel et al 2013a). Some AM-inducible AMTs were detected on the branch domain of periarbuscular membranes, indicating that active NH 4 + transfer occurs around arbuscular branches into the cytoplasm of the arbusculated cells (Guether et al 2009;Kobae et al 2010;Koegel et al 2013a).…”

“…bicolor) and analyzed the AM-inducible AMT SbAMT3;1 in detail (Koegel et al 2013a). We demonstrated that SbAMT3;1 is expressed in cells containing developing arbuscules, suggesting its prime role in the transport of NH 4 + from the fungus to the plant.…”

Identification of arbuscular mycorrhiza-inducible Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in rice

“…In experiment 1, rice plants were provided with modified Hoagland solution containing either no N or 15 mM N. One week after transplanting to pots containing a 1:1 (v/v) mixture of autoclaved zeolithe (Symbion, CZ) and sand, seedlings were inoculated with a 2-g (~100 spores) inoculum of R. irregularis BEG-75 to establish AM symbiosis (Koegel et al 2013a). For non-mycorrhizal plants (non-AMF), the same amount of autoclaved inoculum was added.…”

Influence of different host associations on glutamine synthetase activity and ammonium transporter in Santalum album L.

“…AMT1 gene family was first identified from Saccharomyces and Arabidopsis (Gazzarrini et al 1999), subsequently cloned from Oryza sativa (Suenaga et al 2003), Medicago truncatula (Straub et al 2014), Lotus japonicas (Salvemini et al 2001), Brassica napus (Pearson et al 2002), Lycopersicon esculentum (von Wiren et al 2000), Populus trichocarpa (Couturier et al 2007), Sorghum bicolor (Koegel et al 2013) etc. Among woody plants constitutive organ-specific AMT1 transcription was detected only in Populus (Couturier et al 2007), Citrus (Camanes et al 2007) and Pyrus (Li et al 2015).…”